A photoionization detector (PID) is commonly employed in the detection of volatile organic compounds (VOCs). It utilizes ultraviolet (UV) light to ionize gas molecules and measures electrical signals caused by free electrons and ions. PID systems are highly sensitive and able to detect a wide range of organic compounds and other hazardous chemicals at parts per billion (ppb) levels. PID systems have a relatively long life and do not need frequent replacement. However, since PID systems are sensitive to external factors, e.g., atmospheric pressure and ambient temperature, calibrations are conducted routinely to maintain the measurement accuracy. For instance, after a PID system is moved from one place to another place or the temperature change is beyond a certain range, a calibration is performed. A PID calibration process requires properly trained personnel and a supply of calibration gases. It is time consuming and labor intensive to calibrate a PID system, especially when the system is installed at a location that is difficult to reach (such as above a high ceiling), or dangerous to access (such as inside an underground tank). Therefore, it is desirable to have automated calibrations for a PID system.